Signaling system



April 5, 1938. G. A. PuLLls SIGNALING SYSTEM Filed oct. 31, 1935 Patented Apr. 5, 1938 UNITED STATES 2,113,221 sIGNALmG sYs'rEM Application october 31, 1935, serial `Nai'assmr` 4 Claims.

This invention relates to high frequency signaling over telephone toll lines and particularly to a system for indicating frequency and voltage variations in the high frequency signaling source 5 utilized for signaling purposes;

In voice frequency signaling systems as applied to telephone toll lines interconnecting widely separated telephone exchanges, it is customary to utilize interrupted voice frequency currents for transmitting signals of various characters over the toll lines. The correct functioning of such systems depends, to a considerable degree, upon the faithfulness of the voltage and frequency output of the signalingcurrent source. Itis, therefore, essentiaLin order to insure the accurate transmission of signals over the toll lines, that any departure in the voltage or frequency, from predetermined limits, of the signaling current source, be immediately detected so that means may be resorted to to bring the signaling source back within the permissible limits.

' It is accordingly an object of this invention' to provide a simple, inexpensive and dependable off-frequency and low-voltage alarm circuit which functions in a reliable manner in detecting small changes in the frequency and voltage generated by a source ofalternating current.

A feature of the invention resides in inductively coupling each of a plurality of signaling channels with a common amplifier in the indicating circuit in such a manner that interaction between the several channels is eliminated.

This and other features of the-invention will be readily understood from the following detailed description made 'with reference to the accompanying drawing which illustrates an offfrequency and low-voltage alarm circuit embodyling the features of thiskinvention. 40 A pair of telephone toll lines are shown at A and B, the first line A being supplied with voice' frequency signaling current from the winding I0 of the 1000 cycle generator II and the line B being furnished with signaling current of the same frequency from the generator winding I2. Interposed between the generator windings I0 and I2 and their respective toll lines A and B are interrupters I3 and I4 which are shown to be 180 degrees out of phase with each other and are adapted to set up interruptions in the signaling current source at the rate of 20 cycles per second. The lines A and B are accordingly alternately supplied with 1000 cycle current interrupted at 20 cycles which is utilized in the well- 55 known manner in effecting the operation of 1000 cycle current which is interrupted at the PATENT OFFICE (ci. rxr-311) signalingequipment (not shown) associated with the lines A and B; v

The input terminals of a balanced bridge type rectifier I3 are connected acrossV the generator winding Il at the pointsii and yIIi while the input terminals of a similarfrectifier 20V are connected across the generator winding I2 at the points I land I3. Oneof the outputterminals of rectifier I3 is connected tov an output terminal of rectifier 20 by way of the primary winding 10 f o'f transformer 2|, the other output terminals of the rectiflers being connected directly' by the. conductor 22. I. .Y

. The .windings I Il and I2 ofgenerator- IfIsupply rate of 20 cyclesper 'second by means'of the interrupters I3 .and I4. However, vthe interruptions of winding In are exactly degrees vout of phasewith'the interruptionsof-winding I2 with the result that steady rectified v1000 cycle 20 vcurrent is-applied to the primary Awinding of transformer 2|. 'I'his rectitled'current' appears as 2000.fcy'cle current onlthelsecondary side of thetransfor'mer 2I and is impressed on'the grid electrode of the amplifier 23.' 25

A retard coll 24 and a vcondenser 25 constitute a tuned circuit connectedacro'ss the transformer secondary by way of the 'resistances 26 and21, which is tuned anti-resonant to 2000 cycles and attenuates all frequenciesother than 30 2000 cycles. V if l The plate circuit of amplifier-fn lincludes' the primary winding of transformerZB; the secondary of which'is associated -with thevoltage dou-I bling combination comprising vvr'ectiflers 30, 3|' 35 and condensers 32, 33. The amplified current, or output of the amplifier '23 is accordinglyl impressed on the rectifiers 30 and'3l which,as above indicated, arearranged `with condensers 32 and 33 for voltage doubling. 40

`The rectified voltage, or outputof lthe', rectifier-condenser combination, is impressed on the control gap of the-cold cathode' gas-filled tube 35 by way of resistance with such, a polarity as to oppose the normal voltage applied to the 45 control gap by battery 38 and with a voltage of sumcient value to reduce the normal control gap voltage below the breakdown or ionization point of the gap. The tube 35, underthese conditions, does not fire and the alarm relay 4I)k ac- 50 cordingly remains unoperated. The normal biasing potential of battery 38 is applied to the ungrounded cathode of tube 35 by way of the two rectifiers 30 and 3l and the resistance 36, it being understood that, in this instance, the rectifiers 55 merely act as high resistances. Though shown poled to oppose the flow of current from the battery 38 the rectiers do not present an infinite resistance. The condenser 31 serves to shunt out the high frequency components of the rectied voltage thereby preventing the breakdown` of the tube on the peaks of these high frequencies and the consequent untimely operation of the alarm. The` condenser also prevents the tube from breaking down on other `transient currents.

When the frequency of the generator falls below 980 cyclesv or exceeds 1020 cycles the antiresonant circuit, comprising retard coil 24 and condenser 25, attenuates the voltage applied to the grid of the tube 23 with the result that the voltage output of the transformer 28 is decreased. The lower value of rectified voltage which is now applied to the control gap of the tube 35 is not of a sufficient magnitude to reduce the normal voltage, applied by battery 38, below the ionization point of the control gap of the tube. The tube control gap accordingly ionizes and the main gap also ionizes as a result of the breakdown of the control gap. Relay 40, which is included in the output circuitof the tubes 35 accordingly operates completing an obvious circuit for the audible and visual signals 4I and 42 respectively. To restore the relay 40 the lead to the relay from the plate electrode of tube 35 may be carried through the contacts of key 60, operation Yof the key 50 restores the relay and deionizes the tube.

Since any departure in frequency from the predetermined frequency of the source II resultsin a corresponding drop in voltage across the input of amplifier 23 due to the attenuation effect of the tuned circuit including retard 24 and condenser 25 with the result that an alarm signal is brought in, it follows that any drop in voltage at the generator terminals will effect the same result. The system so far described, therefore, functions not only as anon-frequency indicator but also as a low-voltage indicator.

It will be noted that during the period in which the generator winding III and interrupter I3 are functioning to transmit signaling current over the line A, the signaling current in the channel C traverses a` path extending from the point I5, conductor l5, rectifier element 46, primary winding of transformer 2l, thence through the four balanced arms of rectifier 20 in parallel, conductor 22, rectifier element l1 and back to the point I6. Due to the fact that the bridge 20 is balanced there will be a zero difference of potential across the channel D, it being also understood that when the interrupter I3 is in such a position as to permit the signaling current to pass, the interrupter I4 is in a position to preventits passage; in other words, duringthe transmission of signaling current over one of the channels C, or D, the other channel experiences a silent interval. It is evident, therefore, that during the effective interval on channel C, the channel D is rendered immune to any disturbance which might otherwise be caused by the leakage of the 1000 cycle current from the channel C by way of the primary winding of transformer 2|.

During the silent interval on channel C, signaling current from generator winding I2 traverses a path from the point I1, conductor 50, rectier element 48, conductor 22, the four balanced arms of the bridge I9, primary winding of transformer 2|, rectifier element I9 to the point I8. Under this condition, due to the balanced condition of bridge I9, the 1000 cycle current transmitted from the generator winding I2 is prevented from leaking back into the channel C. Such leakage, if not eliminated, would cause undue disturbances on the toll lines A and B and other circuits associated therewith.

What isA claimedv is:

1. In a signaling system, a plurality of signal channels, a balanced bridge for each of said channels havinginput and output terminals, each of said channels being connected to the input terminals of its respective bridge, an amplier and a transformer inductivelycoupling said channels with said amplifier, the output terminals of said balanced bridges being connected in a series circuit including a primary winding of said transformer.

2. In a signaling system, a plurality of signal channels,`a source of signaling current, means for transmitting current of a predetermined frequency from said source alternately over said signal channels, an amplier, means for inductively coupling said amplifier to all said signal channels and means for rendering one of said channels immune to leakage current from another of said channels by way of the coupling means, said means comprising a balanced bridge type rectifier for each of said channels having their input terminals connected across their respective signal channels and their outputterminals connected in a series circuit including a portion of the coupling means.

3. In an electric circuit arrangement, a signaling channel terminating at the input terminals of a balanced bridge, a second signaling channel terminating at the input terminal. of a second balancedbridge, an ampliery common to said channels and a transformer for coupling said amplier to said signaling channels, an output terminal'of said' rst bridge being directly connected to an output terminal of said second bridge and the other output terminal of said rstbridge being connected to the other voutput terminal of said second bridge by way of a winding of said transiormer.

4. In a signaling system, a pair of current conducting channels alternately carrying. current from a signaling current source and each of said channels terminating in a 'balanced bridge, an amplifier common to said channels and a transformer for coupling said channels to said amplier, the path for the current transmitted over one o1' said channels from said source including of said channels terminate.

GEORGE A. PULLIS. 

